DESCRIPTION: (Adapted from applicant's description) The goal of this research is to establish a biomarker of ambient lead (Pb) exposure during prenatal and postnatal development, which, in turn, can be used to study synchronic teratogenic effects of Pb on brain development and other systems. To do so, the investigators will try to: (a) label Pb absorption in tooth enamel of rats using stable isotope and radioisotope, (b) measure radio labeled histological cross sections of rat tooth enamels to determine distribution of tracer Pb, (c) analyze lead concentration of histological cross sections of rat tooth enamels by ion microprobe spectrometry, and (d) confirm specificity and sensitivity of label absorption in the formation and maturation of enamel tissues.